Feature

Climate science: fact from fiction

Confused by conflicting reports on global warming? Get the facts on climate science.

Credit: iStockphoto

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When it comes to global warming and climate scientists, one thing is for certain: the public attitude has definitely cooled.

A string of controversies - including leaked emails from scientists accused of manipulating data, errors over Himalayan glacier melt by the Intergovernmental Panel of Climate Change (IPCC), and the retraction of an important paper on sea level rise - has led to a sharp drop in the number of people who accept the climate threat.

Earlier this year, the UK government's chief scientist, John Beddington, urged scientists to be more open about what they can and cannot be sure of. He told The Times newspaper, "There is a fundamental uncertainty about climate change prediction." But Beddington, like many other leading scientists, has repeated his conviction that the basic science behind human-induced global warming is correct.

The IPCC's last report involved gathering 90,000 comments from about 2,500 reviewers on more than 10,000 papers - the overwhelming majority of which support climate change as a real phenomenon. Sceptics who seize on rare mistakes or individual papers or events that don't seem to support climate change are guilty of misrepresentation, say their critics.

"A single study is never definitive," points out Steve Sherwood of the Climate Change Research Centre at the University of New South Wales in Sydney. "The conclusions the scientific community has reached are the result of a long, long process over decades of looking at the evidence. As an atmospheric scientist, I don't know any colleague that will deny that greenhouse gas emissions are having a warming effect," he adds. "They may differ on the magnitude of that effect, but not on the effect."

So what is the evidence for climate change?

Warmer temperatures

In November 2009, emails from scientists at the Climatic Research Unit at the University of East Anglia in the UK were stolen by hackers and leaked to the media. One of the most apparently damaging comments had been sent by Phil Jones, then director of the unit, in 1999. He wrote: "I've just completed Mike's Nature trick of adding in the real temps to each series for the last 20 years (ie from 1981 onwards) and from 1961 for Keith [Briffa's] to hide the decline."

Jones was referring to a recent supposed - not actual - decline in temperatures suggested by a study of tree rings. Historically, changes in temperature correspond well with tree rings, but this isn't the case for the past 50 years or so, and scientists don't know why.

The "trick" was a previously published method by Michael Mann at the University of Virginia, USA, that merged data from tree rings and thermometer readings. Jones did not have evidence of global cooling that he was trying to conceal, as some sceptics have claimed; he was instead trying to include the more accurate temperature recordings.

FACT:

Over the last 100 years, the average global surface temperature has risen by about 0.74°C. Since the 1970s, it has risen by about 0.4°C, according to the IPCC. Australia's Commonwealth Scientific and Research Organisation (CSIRO) reports that some parts of our country have warmed by 1.5 to 2°C since the 1960s and there have been fewer cold days in that time.

In Australia, 2009 ended the warmest decade on record, according to data compiled by the government's Bureau of Meteorology. The mean temperature for the year was 0.9°C above the average for 1961-1990, and it was the second warmest year since high-quality records began, in 1910.

Satellite data shows that, globally, last November, December and January were the hottest in just over 30 years of such records. "People sometimes suggest that satellite data shows that warming has stopped," says Neville Nicholls, president of the Australian Meterological and Oceanographic Society. "In reality, it shows the opposite. Warming continues despite rumours of its demise."

What about the recent freeze in parts of Europe and the US? In fact, the recent cold weather was within the bounds of natural variability, and still adhered to the global trend of rising temperatures, according to the UK's Met Office. And while the UK, Siberia and parts of the US were colder than average last December and this January, other regions of the northern hemisphere, such as Alaska, Canada and the Mediterranean were warmer than usual.